The present embodiments relate to magnetic resonance tomography devices and methods for phase-correcting postprocessing of data acquired using a magnetic resonance tomography device during a parallel transmission using a plurality of transmitting devices.
Magnetic resonance tomography devices are described, for example, in DE 102008023467 and U.S. Pat. No. 7,592,813.
In an MR imaging system, transmit phases (or time characteristics of transmitted signals) generated at every point of an area (e.g., a FoV or part of the FoV) may be given by the RF transmission profile of a coil. Phase relationships of transmitted signals generated by RF pulses in different voxels (e.g., three-dimensional points having a small volume) remain constant in time (e.g., during the application of each of the transmitted RF pulses). Global phase offsets, as used, for example, in RF spoiling, are spatially independent and may be corrected by a corresponding phase correction in the receiver or in the data postprocessing using a spatially independent phase correction. Global may be applicable to all transmitters.
In the case of a plurality of transmitters operated in parallel, the resulting B1 field may be varied in phase and amplitude in space (e.g., RF shimming) by adjustment of the phases and amplitudes of each individual transmitter. Phases induced via the RF excitation, which change locally from recording to recording (of an imaging session using the MRT system), overlay one another with the signal phases superimposed for spatial encoding and lead to spatial misregistrations and artifacts.
Spatial distribution of the (e.g., entire) RF field may not change (except for a global phase and amplitude) from one recording to the next. All (corresponding) pulses used for signal generation use the same phase and amplitude responses for the individual transmitters for each recording.
Individual RF pulses are optimized in terms of one criterion and are applied unchanged (except for a global phase and amplitude) in each recording. In conventional imaging using one transmit channel, the global phase and amplitude are a degree of freedom for exerting an influence of the resulting field. The phases generated during the signal generation may also be varied using gradients switched during the transmission. The multidimensionally selective pulses, which simultaneously modulate the gradient amplitude and RF envelope, are also not changed from recording to recording.